The use of all electrical or electronic devices or instruments is prohibited except for the following
functions: time keeping, compass heading and changes thereof, or the recording of sound or photographic images.
This means that the tacktick micro compass is allowed but the racemaster is not. If you have a GPS on board it cannot be used whilst racing but if it was switched on and unavailable whilst racing you would at a later stage be able to look at your track. If you then use this information to help plan the next race of the day then you are in breach of the rule. For those sailors who use their GPS to record their route, and then let it be known, then they are at risk of being protested. Far better not to take the risk.
I have a nexus 7 fully loaded with raster charts and I use it as a chart plotter. It is very plain to see if you are being headed or if you get a lift. It is also very good for spotting the lay line to the next mark. It was these sort of functions the CWA had in mind when formulating the proposed rule change.